yeah, i wounldnt think it could sustain numbers in the mid 500s for long. I know f8tl's z71 according to his numbers was pushing close to 550rwhp(i believe, correct me if im wrong f8tl) that was with a gt 67 and 6.0 heads i think.

I really do not know how much horse power the 5.3 / 6.0 crank can take.

the 5.3 / 5.7 / 6.0 come with the same size crank shaft, some on here and ls1tech have had 500 to 600 horses on the stock crank, so far no one has broke one yet from too much horse power, and no one has found out just how much horse power these cranks can hold up to.

the book states 550 horses, but we know that is a lie because too many have pushed far more horse power then that, I would not be surprised if the stock crank was not equal to a forged crank and can hold up to 700+ horses with no problem.

For $400 I would say go the 5.3 route and spend the rest on a GT67 turbo The 6.0 has more potential for power but you are gonna spend way more trying to find one and its gonna suck down gas like there is no tommorrow.

I only put about 5k miles on the setup around the 500rwhp range. The 550ish I was pushing at the track was only because I put race gas in and turned up the boost from 13-14 to 14-15.

I think what it will come down to is having good luck and getting a solid stock motor. Obviously not all are built exactly the same and some parts may be inherently weaker (flawed castings etc) than others and could give at much lower HP levels. Also the stress put on those parts by varying loads (3400lb car vs 6000lb SUV).